The present invention relates generally to a sensor with a dynamic latch and more particularly to a sensor with a dynamic memory to allow for full performance with low power and multiplexed applications.
Low power sensors are used in a variety of applications where the conservation of supply current is a priority, such as in battery-operated equipment. An exemplary low power sensor is a magnetic sensor which uses, for example, a Hall effect element for the transducer, and which provides broad versatility in position sensing applications. For example, a Hall sensor could sense the proximity of a small magnet in a cellular flip-phone. When the cover is opened, the sensor signals the cell phone controller to begin the appropriate actions desired by the user, such as illumination of the keyboard. Subsequently, closure of the cover terminates the phone call and returns the phone to a low power, standby state awaiting incoming calls. Typically, the Hall effect sensor also provides a xe2x80x9chysteresisxe2x80x9d function for such position-sensing applications, toggling its magnetic threshold between an xe2x80x9cOperatexe2x80x9d (ON) level and a xe2x80x9cReleasexe2x80x9d (OFF) level. This function tends to eliminate the output uncertainty arising from vibrations or electrical noise as the sensor approaches its switching point.
Ideally, the standby state of sensors in such a system requires xe2x80x9czeroxe2x80x9d current for optimum battery life. Present approaches for power conservation employ on-chip clock circuitry that momentarily activates the sensing circuitry for a small percentage of the duty cycle. Thus, the average current utilized by these devices is much lower than a similar device with continuous excitation. However, the clock circuit and some form of memory to xe2x80x9crecallxe2x80x9d the last state of the sensor need continuous power to achieve the aforementioned hysteresis function.
A photodetector circuit described by Johnson et al. in U.S. Pat. No. 5,151,591 and a Hall circuit implemented by Vig in U.S. Pat. No. 5,619,137 are two examples of strobed sensors in which power is periodically applied by a system controller. However, the designs according to these patents do not have the necessary elements for full performance with complete interruption of the power source.
The present invention allows complete power-down during OFF periods by providing a xe2x80x9cdynamicxe2x80x9d memory (or a memory that xe2x80x9crefreshesxe2x80x9d with momentary power application).
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
According to one aspect of the present invention, a sensor dynamic latch arrangement comprises a sensor, first and second nodes coupled to the sensor, a regenerative latch, and an output stage. The regenerative latch is arranged to couple the first and second nodes to third and fourth nodes. The regenerative latch provides output signals on the third and fourth nodes dependent upon input conditions on the first and second nodes. The regenerative latch is arranged to remember the output signals upon a power interruption, and the regenerative latch is arranged to regenerate the input conditions and the output signals following the power interruption. The output stage is coupled to the third and fourth nodes.
According to another aspect of the present invention, a sensor dynamic latch arrangement comprises a sensor, a summer, a regenerative latch, and an output stage. The summer has a first input coupled to the sensor. The regenerative latch is coupled between an output of the summer and a second input of the summer and having an output. The regenerative latch is arranged to remember a signal on its output upon a power interruption, and to regenerate the signal following the power interruption. The output stage is coupled to the output of the regenerative latch.
According to a further aspect of the present invention, a sensor dynamic latch arrangement comprises first and second input nodes, first and second output nodes, a sensor, first and second amplifiers, and first and second energy storage devices. The sensor is coupled to the first and second input nodes. The first amplifier is coupled between the first input node and the second output node, and the second amplifier is coupled between the second input node and the first output node. The first energy storage device is coupled to the first output node and the second energy storage device is coupled to the second output node so that the first and second energy storage devices remember signals on the first and second output nodes upon a power interruption, and so that the first and second energy storage devices regenerate the signals on the first and second output nodes following the power interruption.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.